Rigid and non-rigid connections between implants and teeth: biological and technical complications.


In certain circumstances, it may be an option to join a natural tooth (either already heavily restored or crowned) and dental implant to create a tooth-implant (T-I) fixed prosthesis. This may be due to anatomical restrictions, patient’s wishes or financial considerations. Though still considered by some a controversial treatment option a systematic review published in 2012 (Pjetursson, Thoma, et al. 2012) calculated the 5 and 10-year survival rates of 95% (95% CI: 91.5-97.6) and 77.8% (95 CI: 64.9 – 86.2) respectively. The major concern voiced in the literature was the differential mobility between the ossoeintigrated dental implant and the periodontal ligament of the natural tooth causing intrusion (Garcia & Oesterle 1998).

The main aim of the review was to assess the impact of rigid and non-rigid connectors between natural teeth and implants on the biological, functional and/or the prosthetic complication rates. (Tsaousoglou et al. 2016)


The review followed the PRISMA statement (Moher et al. 2009). Searches were conducted by two independent reviewers in Medline, Embase, Google Scholar Beta and Cochrane databases. Dates were limited to January 1980 to August 2015. In addition, they conducted a hand search of high impact journals in the field of implant retained prosthodontics. Eligibility criteria were randomised clinical trials(RCTs) (I-IV), and prospective, retrospective cohort studies published in English. Two reviewers independently selected studies for inclusion, abstracted data and assessed risk of bias using a modified version of the Cochrane Collaboration tool for assessing risk of bias (Higgins JPT et al. 2011). The primary outcome measures were biological and/or prosthetic (technical) complications rates, secondary outcome measures were not stated.


  • 10 studies fulfilled the inclusion criteria (4 prospective cohort studies, 6 retrospective cohort studies)
  • The overall quality of evidence of the 10 studies was low.
  • A total of 481 patients received 526 FDPs supported by 981 abutment teeth connected with 1072 implants.
  • The mean follow-up period of the three studies which were eligible for inclusion in the meta-analysis ranged from 18 to 78 months.
  • Primary outcomes
    • Survival rates: (after follow-up periods with a mean range of 18–120 months)
      • Implants 90% -100%
      • Abutment teeth 94.1% – 100%,
      • Prostheses 85% – 100%
    • Biologic complications:
      • Periapical lesions 11.53%
      • Caries 5%,
      • Tooth intrusion 5%
      • Tooth fractures 3.84%,
      • Loss of osseointegration 2.7%
      • Periodontal pathology 2.32%
      • Fistula 1.16%.
    • Technical complications
      • Porcelain occlusal fracture 16.6%
      • Screw loosening 15%
      • Prosthesis remake 10.5%
      • Cement failure/screw fractures 7.98%
      • Tooth intrusion
        Pooled (fixed effect): Effect size 4.862 (0.584/40.501) favouring a rigid connection


the authors concluded:

Within the limitations of this systematic review and meta-analysis, the following conclusions
can be drawn. The tooth–implant FDP seems to be a possible alternative to an implant-supported FDP. There is limited evidence that rigid connection between teeth and implants present better results when compared with the non-rigid one. The major drawback of non-rigidly connected FDPs is tooth intrusion.


This was an interesting review as it tells us more about the problems endemic in dental implant research than it tells us about tooth implant survival.
Firstly it was surprising to note in the introduction the absence of Pjetursson’s (Pjetursson, Zwahlen, et al. 2012) review on T-I survival and complications considering its close association with the University of Bern and the reference to hand searching the Journal of Clinical Periodontology. There may also have been issues with searching the electronic databases for appropriate keywords (Layton 2016; Layton & Clarke 2015).
Many of the systematic reviews state that they are written according to PRISMA guidelines (Chapman et al. 2016) but run into problems in the results section. In this case, there were too many inclusion criteria in the data extraction that did not directly relate to answering the research question. This caused problems with summarising in a clinically relevant format the outcome data, survival rates, and effect sizes.
The authors concluded early on that there were no RCTs but employed the Cochrane Collaboration tool for assessing risk of bias for RCTs, even though the Cochrane Handbook suggests using the Newcastle-Ottawa Scale to assess non-randomised observational studies (Seehra et al. 2016).
In the results section the survival and complication rates are very precise (4 significant figures) but decoupled from any time-frame so it is unclear if a 5% probability of a complication is over 12 months or 10 years.
The meta-analysis for intrusion only included 2 small studies so while they indicate that 8% of the total non-rigidly connected teeth intruded vs. no tooth intrusion in the rigid connection group the summary data should be treated very cautiously because of the limited quality of available studies.
In conclusion, many of the problems originate from the limited quality of the primary research and highlight that in order to have good quality secondary research we need to have good quality primary research, and an over reliance on retrospective studies in restorative dentistry is hampering the search for good quality evidence.


Primary Paper

Tsaousoglou, P. et al., 2016. The effect of rigid and non-rigid connections between implants and teeth on biological and technical complications: a systematic review and a meta-analysis. Clinical Oral Implants Research, pp.1–15.

Other references

Chapman, S.J. et al., 2016. Longitudinal analysis of reporting and quality of systematic reviews in high-impact surgical journals. British Journal of Surgery, pp.198–204.
Garcia, L.T. & Oesterle, L.J., 1998. Natural Tooth Intrusion Phenomenon With Implants: A Survey. Int J Oral Maxillofac Implants, 13(13), pp.227–231.

Higgins JPT et al., 2011. The Cochrane Collaboration’s tool for assessing risk of bias in randomised trials. British Medical Journal, 343, pp.889–893.
Layton, D., 2016. How to Find Dental Survival Articles: Using the New Search Strategies. The International Journal of Prosthodontics, 29(2), pp.135–138.

Layton, D.M. & Clarke, M., 2015. Will your article be found? Authors choose a confusing variety of words to describe dental survival analyses. Clinical Oral Implants Research, 26(1), pp.115–122.

Moher D, Liberati A, Tetzlaff J, Altman DG; PRISMA Group.. Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. PLoS Med. 2009 Jul 21;6(7):e1000097

Pjetursson, B.E., Thoma, D., et al., 2012. A systematic review of the survival and complication rates of implant-supported fixed dental prostheses (FDPs) after a mean observation period of at least 5 years. Clinical Oral Implants Research, 23(SUPPL.6), pp.22–38.

Pjetursson, B.E., Zwahlen, M. & Lang, N.P., 2012. Quality of reporting of clinical studies to assess and compare performance of implant-supported restorations. Journal of Clinical Periodontology, 39(SUPPL.12), pp.139–159.

Seehra, J. et al., 2016. Use of quality assessment tools in systematic reviews was varied and inconsistent. Journal of Clinical Epidemiology, 69(September), pp.179–184.

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